Dynamic Stability of a Cantilever Boring Bar with Machined Flats under Regenerative Cutting Conditions

Abstract

The paper is concerned primarily with the stability of a slender boring bar which can be represented at the tool point by a simple two-degree-of-freedom, mass-spring-damper system. Its purpose is to determine how the vibration behaviour during machining is affected by coupling between modes.The stability behaviour is investigated for machining processes in which the cutting operation is of the regenerative type, when successive passes of the workpiece cause cuts to overlap. Account is taken of variations in certain system parameters, including the effect of workpiece speed, and results derived from practical cutting tests are described. Particular attention is paid to the effect on chatter-free machining performance of variations in the angle of setting of the boring head relative to the two planes of vibration.A theory is developed to apply the basic principles of the coupling mechanism over a wide range of conditions. Predicted changes in chatter characteristics are compared with experimental observations.Certain discrepancies arise between theory and practice, some of which can be resolved by re-assessing the initial assumptions for cutting forces.